Error detecting mechanism for servosystem

Abstract

The invention relates to a mechanism wherein a relative rotary angle of a driving motor is detected by use of an encoder, and, if an error occurs in a servo control action when the driving motor is servo-controlled in accordance with a deviation value of the relative rotary angle from a desired rotary angle of the driving motor, then the servo control action is brought to an emergency stop. A potentiometer for detecting an absolute rotary angle of the driving motor is connected to a rotary shaft of the driving motor and said emergency stop is effected when a difference between said absolute rotary angle and said relative rotary angle exceeds a preset tolerance value, so that an error in the servo control action can be reliably prevented.

What is claimed is: 
     
       1. An error detecting mechanism for a servosystem, comprising: a rotary angle detecting system including an encoder connected to a rotary shaft of a driving motor, for detecting a relative rotary angle of said driving motor and a potentiometer for detecting an absolute rotary angle of said driving motor; a driving-controlling system for driving and controlling said driving motor in accordance with a deviation value of a rotary angle detection value of said driving motor from a desired rotary angle; and an error preventing system for preventing a malfunction of said driving-controlling system; said error preventing system being provided with an emergency stop control circuit for effecting an emergency stop of said driving motor when a deviation value between said relative rotary angle detection value detected by said encoder and said absolute rotary angle detection value detected by said potentiometer exceeds a preset tolerance value. 
     
     
       2. An error detecting mechanism for a servosystem as set forth in claim 1, wherein said encoder is a rotary encoder. 
     
     
       3. An error detecting mechanism for a servosystem as set forth in claim 2, wherein said rotary encoder and said potentiometer are connected through a reduction gear to a shaft opposite to the drive shaft of said driving motor. 
     
     
       4. An error detecting mechanism for a servosystem as set forth in claim 3, wherein said driving motor is a DC motor. 
     
     
       5. An error detectting mechanism for a servosystem as set forth in claim 4, wherein said DC motor is provided at a joint portion of an arm of the industrial robot, for driving said arm. 
     
     
       6. An error detecting mechanism for a servosystem as set forth in claim 5, wherein said DC motor, rotary encoder and potentiometer are housed in one and the same motor unit. 
     
     
       7. An error detecting mechanism for a servosystem as set forth in claim 6, wherein said rotary angle detecting system includes a counter adapted to be reset when the industrial robot is started in operation, and thereafter, to count pulses outputted from said rotary encoder. 
     
     
       8. An error detecting mechanism for a servosystem as set forth in claim 7, wherein said rotary angle detecting system includes an A/D converter for converting an analogue detection value outputted from said potentiometer into a digital signal. 
     
     
       9. An error detecting mechanism for a servosystem as ser forth in claim 8, wherein said error preventing system includes a comparator for digitally comparing the relative rotary angle detection value outputted from said counter with the absolute rotary angle detection value outputted from said A/D converter. 
     
     
       10. An error detecting mechanism for a servosystem as set forth in claim 9, wherein said error preventing system includes an emergency stop control circuit for outputting an emergency stop command signal to said DC motor when a deviation value outputted from said comparator exceeds the preset tolerance value. 
     
     
       11. An error detecting mechanism for a servosystem as set forth in claim 10, wherein said error preventing system includes a brake for braking said DC motor and a contact for being `ON` operated in response to a command signal outputted from said emergency stop control circuit to supply a driving current to said brake. 
     
     
       12. An error detecting mechanism for a servosystem as set forth in claim 11, wherein said driving-controlling system includes a rotary angle commanding circuit for commanding a rotary angle of said DC motor, a comparator for comparing the relative rotary angle detection value from said counter with the desired rotary angle from said rotary angle commanding circuit, an D/A converter for converting a deviation value of the relative rotary angle detection value from the desired rotary angle outputted from said comparator into an analogue signal and a driver for driving said DC motor in accordance with the deviation value converted into an analogue signal. 
     
     
       13. An error detecting mechanism for a servosystem as set forth in claim 12, wherein said error preventing system includes a contact for being `OFF` operated in response to a command signal outputted from said emergency stop control circuit to cut off the current supplied to said driver. 
     
     
       14. An error detecting mechanism for a servosystem, comprising: a rotary angle detecting system including a rotary encoder connected to a rotary shaft of a DC motor for driving an arm of a industrial robot for detecting a relative rotary angle of said DC motor and a potentiometer for detecting an absolute rotary angle of said DC motor, said rotary encoder and said potentiometer being connected through a reduction gear to a shaft opposite to the drive shaft of said DC motor; a driving-controlling system for driving and controlling said DC motor in accordance with a deviation value of a rotary angle detection value of said DC motor from a desired rotary angle; and an error preventing system for preventing a malfunction of said driving-controlling system, said DC motor, said rotary encoder and said potentiometer being housed in one end of the same motor unit, said rotary angle detecting system including a counter adapted to be reset when the industrial robot is started in operation to count pulses outputted from said rotary encoder, and includes an A/D converter for connecting an analogue detection value outputted from said potentiometer into a digital signal.